This invention is concerned with a medical probe for use in registering and influencing tissue activities. Especially meaningful are the thin film probes, called electrode probes or transducer probes, used in medical research as well as in human medicine in order to determine or to influence electrical activities of the tissue, metabolic activities, blood flow, ion and molecular changes, etc.
Thin film probes are qualified in particular for multiple recordings because of their possible variation in design and dimension (O. Prohaska, F. Pacha, P. Pfundner, H. Petsche: A-16-fold semi-microelectrode for intracortical recording of field potentials, Electroenceph. Clin. Neurophysiol. 47, 629-621, 1979).
One previously known medical electrode, disclosed in Austrian Patent No. 342,189, consists of a non-conducting body that carries on one end a contact electrode which is connected to a lead within the non-conducting body. In addition, a throw-away enclosure of non-conducting material is mounted around the individual reusable electrode. Within the cover is a cavity which borders on the contact electrode as well as on the outer area by at least one aperture in the throw-away enclosure and is filled by a viscous electrolyte. This type of structure provides for direct contact between the material under test and the metal or intermetallic compound electrodes and/or transducers which cause some serious disadvantages:
(a) the electrode impedance varies as an inverse function of the electrode area (H. J. Vetter: Elektrochemische Kinetik, Springer Verl. Berlin, 1961) and, therefore, miniaturization of the electrode(s) results in unacceptably high electrode impedance; PA0 (b) polarographic recordings (I. M. Kolthoff, J. J. Lingane: Polarographie, Intersci, Publ. N.Y., 1952) cause a current flow through the tissue which irritates and, frequently, injures the tissue, PA0 (c) the extracellular ion and molecular concentration is only recordable under stable conditions which, unfortunately, seldom exist, PA0 (d) ion concentration changes in the material under test often alter potential recordings within the tissue; for instance: Cl.sup.- concentration changes cause the electrode potential change of an Ag/AgCl electrode to change.